Geomorphology

Text by dr. A.C. Seijmonsbergen, Institute for Biodiversity and Ecosystem Dynamics, University of Amsterdam.

geomorfologic map a-Pano-2

Geomorphological map of the Sierra Nevada del Cocuy (Van der Hammen et al., 1980/1981) 

The Cocuy Mountain Range is characterized by distinct landforms and processes typical for high Andean geomorphology, such as glacial valleys, cirques, moraines, meltwater deposits, and a variety of younger landforms and processes related to mass movements. The surface drainage network is highly disturbed by the recent glaciations, which is witnessed by numerous glacial lakes, wetlands and associated peat growth. The repeated glaciations during the Quaternary have left a wealth of deposits, especially in the highest parts of the Cocuy Range (Kraus & van der Hammen 1960, González et al. 1965; van der Hammen et al. 1980/1981). Van der Hammen et al. (1980/1981) identified at least five (possibly six) glacial depositional phases, which were classified according to their relative age and material assemblages into so-called Drift: Drift 2-5 were formed during the Last Glacial age. Drift 6 marks the Neoglacial and the actual superpáramos (see Glacial Morphology map of Van der Hammen et al. 1980/1981). Each drift sequence was subject to weathering and has developed unique soil properties, which may nowadays dictate the general distribution of the vegetation cover. For example, the upper grass páramo follows more or less the border between Drift 5 and 4, while the lower grass and shrub páramo presently extend over the area of Drift 3. The present-day upper forest line seems to follow the border between Drift 2 and 3. The younger the Drift sequence, the more intact are the material and landforms: landforms and materials of older glaciations have been largely eroded by younger processes, which hampers detailed landscape reconstructions. Noteworthy is the high pass at the eastern side of the Cocuy massif, Boquerón de la Sierra (at 4550 m), which was covered under snow and ice at least up to 40 years ago according to aerial photographs taken in 1955 and 1959. The geomorphological map of Van der Hammen et al. (1980/1981) has been based on these aerial photos. Today permanent snow and ice are absent at this pass, and many small glaciers show signs of recent melting on Google Earth, which indicates a negative glacier mass balance, as the probable result of rising temperatures in this region. Other geomorphological effects are related to reduction of meltwater which may affect land use in the area and may have irreversible consequences for the paramo vegetation.